Shanghai authorities are trying to assure people of China's largest city that their drinking water is safe despite finding nearly 6,000 dead pigs in the river that provides water to the city's taps.

Shanghai residents were further unnerved when health officials determined that the pigs were infected with a disease known as porcine circovirus, but health officials insisted that it does not affect humans.

The pig bodies were found in the Huangpu River about 40 miles north of Shanghai's 23 million residents, raising fears that they are drinking a "pork broth," as some referred to it in a moment of black humor.

The government has been playing down the incident and reassured citizens that Shanghai tap water samples passed government test and it is safe to drink.

Shanghai authorities used tags on the pigs' ears to trace them to the city of Jiaxing in Zhejiang province, upstream from Shanghai. Jiaxing is the main supplier of pork to China's east coast, with 4.5 million pigs delivered every year.

Jiaxing city government officials denied responsibility for the dead pigs.

"The tags on the pigs' ears only indicate the pigs were born here," argued Jiang Hao, the vice director of Jiaxing's Animal Husbandry Bureau. "It doesn't mean they were raised here. No signs have been found of any epidemic among animals in Jiaxing, and local hogs' mortality rate remains normal."

The government is blaming some farmers in Jiaxing for a lack of environmental awareness, and for carelessly disposing of their dead pigs. The government says it will make every effort to investigate the case and punish anyone who dumped pig carcasses in the river.

Last year, the Jiaxing government started a major crackdown on black market sales of pork from pigs that had died of disease. One farmer told Shanghai's Xinmin News Net that some farmers now just toss the tainted meat into the river since they have nowhere to sell it.

"Some dead pigs weighing more than 25 kilos were still being sold and making it onto people's dinner tables," the farmer said. "But since the government arrested some tainted meat dealers, nobody comes to buy the stuff anymore. So it's normal that there are so many dead pigs in the river," he said.